Heretofore, switching power supply devices are known. For example, PTL 1 discloses a substrate-mounted inverter device in which a semiconductor chip is mounted on a surface of a metal substrate with a ceramic-based substrate therebetween (the semiconductor chip includes switching elements and diodes that constitute an inverter). In this device, the three-phase inverter has an upper arm and a lower arm; the upper arm includes a switching element (high-side switching element), and the lower arm includes a switching element (low-side switching element). A collector of the high-side switching element is mounted on an upper-arm-side wiring pattern, and an emitter of the low-side switching element is mounted on a lower-arm-side wiring pattern. The emitter of the high-side switching element is electrically connected to the collector of the low-side switching element via a beam lead electrode for connecting the upper and lower arms.